This research proposal will generate new non-invasive biomarkers with improved sensitivity and specificity to the biochemical and ultra-structural changes of osteoarthritis (OA) through development of quantitative magnetic resonance (MR) methods which can assess the individual water components of cartilage. Cartilage degeneration in OA is characterized by decreased proteoglycan content and disruption of the highly organized collagen fiber network. Multi-Component Driven Equilibrium Single Shot Observation of T1 and T2 (mcDESPOT) and 3D-Cones are novel techniques for bi-component T2 and T2* mapping which can measure the fractions and T2 characteristic specific to the water components bound to proteoglycan (WPG) and collagen (WCOL) within cartilage. Assessment of the individual water components of articular cartilage may provide a new sensitive and specific method to detect changes in the proteoglycan and collagen constituents of the cartilage macromolecular matrix. In Aim 1 of the proposal, mcDESPOT and 3D-Cones will be optimized for performing bi-component T2 and T2* mapping of cartilage. In Aim 2, bi-component T2 and T2* parameters of cartilage samples obtained from 10 human cadaveric knee joints will be measured at 3T using mcDESPOT and 3D-Cones and compared with biochemical parameters (proteoglycan, collagen, and water content), microstructural parameters (integrity of collagen fiber network measured using second harmonic generation microscopy), and biomechanical parameters (aggregate modulus, permeability, and Poison ratio). We hypothesize that the fraction of water bound to proteoglycan (FPG) will be a strong predictor of the proteoglycan content and compressive stiffness of cartilage, while the fraction of water bound to collagen (FCOL) will be a strong predictor of the degree of disruption of the collagen fiber network of cartilage. In Aim 3 of the proposal, 35 asymptomatic volunteers and 70 patients with varying degrees of knee OA will be imaged at 3T using mcDESPOT, 3D-Cones and other currently available quantitative MR techniques. We hypothesize that bi- component T2 and T2* parameters measured using mcDESPOT and 3D-Cones will be more sensitive than other MR parameters for distinguishing between subjects with and without cartilage degeneration. Successful completion of the project will provide the OA research community with new MR biomarkers which are sensitive and specific to the proteoglycan and collagen components of articular cartilage and which can be used for both the detection and characterization of cartilage degeneration in patients with OA.